1. Field of the Invention
The present invention generally relates to a semiconductor device, a semiconductor device unit and a method of manufacturing a semiconductor device unit, and particularly relates to a semiconductor device, a semiconductor device unit and a method of manufacturing a semiconductor device unit which provides high-density mounting by stacking the semiconductor devices.
A semiconductor device is required to be further miniaturized, to achieve higher operational speed and to be more sophisticated, so as to meet the trend of recent electronic devices. The efficiency in mounting the semiconductor device on a mounting board also needs to be improved.
To achieve the above requirements, a majority of semiconductor devices currently available is of the surface-mounting type in which leads are connected on the surface of the mounting board. Yet, a semiconductor device having higher mounting efficiency is desired.
2. Description of the Related Art
FIG. 1 is a perspective view showing a semiconductor device 1 of the prior art. FIG. 2 is a cross-sectional diagram of the semiconductor device of the prior art taken along a line Axe2x80x94A in FIG. 1. The semiconductor device 1 is disclosed in Japanese Patent Laid-Open Application Nos. 63-15453 and 63-15451.
A semiconductor device 1 shown in FIG. 1 and in FIG. 2 includes a semiconductor chip 2, a resin package 3 for sealing the semiconductor chip 2, leads 4 and a stage 7 on which the semiconductor chip 2 is mounted. Each of the leads 4 has one end connected to the semiconductor chip 2 by a wire 5 and the other end exposed from a bottom surface 3a of the resin package 3 so as to form an external terminal 6. In other words, in semiconductor device 1, all parts of the leads 4 except the external terminals 6 are sealed within the package 3.
In the semiconductor device 1 of the above structure, since the parts forming the external terminals 6 are exposed from the bottom surface 3a of the resin package 3, the amount or length of the leads 4 projecting from the side of the package 3 can be reduced. Because of this, the mounting density of the semiconductor device is increased. Also, in the above structure, it is not necessary to bend the projecting part of the lead and thus a mold utilized for bending is no longer required. Therefore various advantages, for example reduction in the manufacturing cost, are expected.
However, there is a problem in the semiconductor device of the prior art. As shown in FIG. 2, terminals 4a of the leads 4, which are to be connected by wires, are positioned at the side of the semiconductor chip 2. Because of this, the package 3 is large in size, and the semiconductor device 1 can not achieve sufficient miniaturization. Ideally, the size of the semiconductor device is miniaturized so as to be substantially the same as the size of the semiconductor chip. Whereas in the semiconductor device 1 of the prior art, the size of the package 3 is more than twice the size of the semiconductor chip 2.
For a semiconductor device proposed so as to solve the above problem, see Japanese Patent Application No. 4-281951, entitled xe2x80x9cSemiconductor Device and Method of Manufacturing Semiconductor Devicexe2x80x9d. FIGS. 3A-3B show a semiconductor device elated to the above Patent Application.
A semiconductor device 10A shown in FIGS. 3A-3B is provided with a semiconductor chip 11, a resin package 17 for sealing this semiconductor chip 11 and a plurality of leads 14. Each of the leads 14 has an inner end 14a electrically connected to the semiconductor chip 11 and an outer end exposed from a bottom surface 17a of a resin package 17 so as to form an external terminal 16. All parts of the leads 14, except the external terminals 16, are sealed within the package 17. The semiconductor device 10A is characterized in that the plurality of the leads 14 is at least partly overlapped with the semiconductor chip 11 vertically within the package 17.
Because of the above structure, the semiconductor device 10A is miniaturized compared to the semiconductor device 1 shown in FIG. 1 and FIG. 2 by an area of the overlapped part (indicated by an arrow L1 in FIG. 3A). Also in FIG. 3A, the semiconductor device 10A includes a stage 12, an electrode pad 13 and wires 15.
In order to achieve further high-density mounting, semiconductors may be mounted in a vertical stack. However, the semiconductor device 10A shown in FIGS. 3A-3B is not suitable for being mounted vertically in a stack. This causes a problem that further high-density mounting (i.e. three-dimensional mounting) cannot be achieved.
For a semiconductor device proposed so as to solve the above problem, see Japanese Patent Application No. 6-168449, entitled xe2x80x9cSemiconductor Device and Semiconductor Device Unitxe2x80x9d. FIGS. 4 and 5 show a semiconductor device related to the above Patent Application.
A semiconductor device 10B shown in FIG. 4 and in FIG. 5 includes leads 18 each of which has an inner lead part 18a and an outer lead part 18b. The semiconductor device is characterized in that a first terminal 18b-1, a second terminal 18b-2 and a third terminal 18b -c are formed by extending the outer lead part 18boutside the resin package 17 and by bending the outer lead part 18b along a shape of the resin package 17.
The semiconductor device 10B has a structure such that the first terminal 18b-1 is placed on the bottom surface of the resin package 17 and the second terminal 18b-2 on the top surface of the resin package 17. Therefore, it is now possible to mount the semiconductor device 10B in a stack thereby achieving further high-density mounting.
However, the semiconductor device 10B shown in FIG. 4 and FIG. 5 is constructed by simply bending the outer lead parts 18b along the shape of the resin package 17 so as to pull the outer lead parts 18b up to the top surface of the resin package 17. Because of this, the second terminal parts 18b-2 and the third terminal parts 18b-3 are provided in such a manner that they are slightly spaced apart from the semiconductor device 10B (see FIG. 5).
Accordingly, the outer lead parts 18b may be easily deformed when an external force is applied. In such a case that neighboring outer lead parts 18b are short-circuited, or that the second terminal parts 18b-2 and the third terminal parts 18b-3 are offset from the predetermined position, electric connection between the upper and the lower semiconductor devices 10B may not be successful. Therefore, there arises a reliability problem in mounting the semiconductor devices in a stack.
In order to solve the above problem, the whole outer lead part 18b may be embedded in the resin package 17. Before being embedded, the outer lead part 18 is bent, for example, by insert-molding. The surface used for electric connection is exposed from the resin package 17. This structure prevents the outer lead part 18b from being unnecessarily displaced from its predetermined position.
However, when the outer lead parts 18b are embedded in the resin package 17, they are not displaced freely within the resin package 17. For example when there is a temperature rise of the device due to the emission of heat by the semiconductor chip 11, a stress is produced at an interface between the leads 18 and the resin package 17. This is caused by the difference in thermal expansion between the leads 18 and the resin package 17.
The coefficient of thermal expansion of the leads 18 is generally larger than the coefficient of thermal expansion of the resin package 18. Accordingly, when there is a temperature rise as described above, the leads 18 will press the resin package 17. Therefore, in the worst case, cracks may be formed in the resin package 17. Also, when these semiconductor devices are stacked using solder, the above described stress may be applied to the part joined by solder and solder may peel off.
Japanese Patent Application No. 10-209732 discloses a semiconductor device unit having-a stack of a plurality of semiconductor devices which can be selectively operated. The semiconductor device described therein is provided with chip-select terminals and chip-select leads. The semiconductor device is selectively operated when chip-select signals are applied to the chip-select terminals. This is achieved by connecting the chip-select terminals and the chip-select leads by means of wires.
However, with the semiconductor device and the semiconductor device unit described above, it is necessary to individually manufacture the semiconductor devices having different structures. This results in a complicated structure and an increased cost. Also, depending on a wire connection structure, some of the semiconductors are only usable as a component of a semiconductor device unit having a stacked structure, which causes a reduced productivity. Moreover, it is necessary to separately handle the semiconductor devices having the different structures before forming a stacked structure. This results in an increased product controlling cost.
Therefore, there is a need for a semiconductor device and a semiconductor device unit which have a simple structure and can be manufactured with a reduced cost.
According, it is a general object of the present invention to provide a semiconductor device, a semiconductor device unit and a method of manufacturing a semiconductor device unit which can satisfy the needs described above.
It is another and more specific object of the present invention to provide a semiconductor device, a semiconductor device unit and a method of manufacturing a semiconductor device unit which can achieve high-density mounting with high reliability.
In order to achieve the above objects according to the present invention, a semiconductor device includes: a resin package in which a semiconductor chip is sealed, the resin package having a first surface and a second surface opposite to the first surface; a plurality of leads having inner lead parts connected to the semiconductor chip and outer lead parts extending outside the resin package, the outer lead parts being bent along the shape of the resin package so as to form first terminal parts on the second surface and second terminal parts on the first surface; connection means electrically connecting the semiconductor chip and the leads; and a positioning mechanism provided either on the leads or on the resin package, which positioning mechanism positions the outer lead parts by engaging a part of the outer lead parts to the resin package.
In the semiconductor device described above, an electric connection can be made at each of the first surface and the second surface of the resin package.
Therefore, it is possible to vertically stack a plurality of the semiconductor devices, so that the mounting ability of the semiconductor device is improved.
Also, the outer lead parts are positioned by the positioning mechanism which positions the outer lead parts by engaging a part of the outer lead parts. This prevents the outer lead parts from being deformed or short-circuited in a case when an external force is applied to the outer lead parts when assembling or mounting the semiconductor devices.
Moreover, the positioning mechanism operates not by engaging with the entire outer lead parts, but by engaging with a part of the outer lead parts. In other words, the outer lead parts are positioned by the positioning mechanism while being able to be displaced or deformed within the range that deformation or a short circuit will not occur.
Therefore, when there is a difference in the rate of thermal expansion between the leads and the resin package, a stress caused by heating can be released by displacement or deformation of the outer lead parts. Accordingly, cracking of the resin package or peeling of the solder at a mounting position can be positively prevented, thereby improving the reliability of the semiconductor device.
It is yet another object of the invention to provide a semiconductor device which can prevent the outer lead parts from being deformed or short-circuited and can also be employed in a case when the lead pitch is narrowed.
In order to achieve the above object, a semiconductor device includes a resin package in which a semiconductor chip is sealed, the resin package having a first surface and a second surface opposite to the first surface; leads having inner lead parts connected to the semiconductor chip and outer lead parts extending outside the resin package from the second surface, the outer lead parts being bent along the shape of the resin package so as to form first terminal parts on the second surface and second terminal parts on the first surface; connection means electrically connecting the semiconductor chip and the leads; and protrusions formed at four corners of the resin package, the protrusions having a height higher than a surface of the resin package and lower than a thickness of the outer lead parts.
In the semiconductor device described above, an electrical connection can be made at each of the top surfaces and the side surfaces of the resin package.
Therefore, it is possible to vertically stack a plurality of the semiconductor devices, so that the mounting ability of the semiconductor device is improved.
Also, the protrusions will accept the external force applied from the side surface, thereby preventing the outer lead parts from being deformed or short-circuited.
Further, there is no need for forming grooves corresponding to each of the outer lead parts. Therefore, the semiconductor device can also be employed in a case when the semiconductor chips are mounted with high density, that is to say, when the number of the leads is increased and the lead pitch is narrowed.
It is yet another object of the invention to easily form a stack of semiconductor devices and mprove the mounting density of the semiconductor device.
In order to achieve the above object, a semiconductor device unit has a structure in which a plurality of semiconductor devices as described above are stacked in a vertical direction. In this structure, outer lead parts positioned at the first surface of an upper one of the semiconductor devices and outer lead parts positioned at the second surface of a lower one of the semiconductor devices are electrically connected, so as to enable the vertical mounting of a plurality of the semiconductor devices.
It is yet another object of the invention to provide joining material and to join the semiconductor devices more easily compared to the structure in which the joining material is provided after the semiconductor devices are stacked.
In order to achieve the above object, a method of manufacturing a semiconductor device unit having a structure in which a plurality of semiconductor devices, as described above, are stacked in a vertical direction, includes the steps of:
a) providing joining material at parts serving as external connection terminals of the semiconductor device;
b) stacking a plurality of the semiconductor devices which are provided with the joining material; and
c) electrically and mechanically joining neighboring ones of the semiconductor devices using the joining material by implementing heat treatment on a plurality of the stacked semiconductors.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.